According to one embodiment, a data processing system includes a plurality of central processing unit (cpu) subsystems, each cpu subsystem having a plurality of cpus and a plurality of memory controllers, each memory controller corresponding to one of the cpus, a plurality of memory complexes, each memory complex being associated with one of the cpu subsystems, wherein each memory complex comprises one or more branches, a plurality of memory leaves to store data, wherein each of the branches is coupled to one or more of the memory leaves and to provide access to the data stored in the memory leaves, and a replication interface to automatically replicate data received from one of the cpu subsystems to another one of the memory complexes, wherein the received data is to be stored in one of the memory leaves.
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1. A data processing system, comprising:
a plurality of central processing unit (cpu) subsystems, wherein each cpu subsystem includes a plurality of cpus and a plurality of memory controllers, each memory controller corresponding to one of the cpus; and
a plurality of memory complexes, each memory complex being associated with one of the cpu subsystems, wherein each memory complex comprises
a plurality of branches;
a plurality of memory leaves to store data, wherein each of the branches is coupled to one or more of the memory leaves and to provide access to the data stored in the memory leaves, and
a replication interface to automatically replicate data received from one of the cpu subsystems to another one of the memory complexes, wherein the received data is to be stored in one of the memory leaves; and
an ethernet switch fabric coupled to each of the memory controllers of the cpu subsystems and each of the branches of the memory complexes, wherein each branch of each memory complex that is associated with one of the cpu subsystems is connected to another branch of another memory complex that is associated with another cpu subsystem and can communicate with each other through the ethernet switch fabric, and the data is replicated via the ethernet switch fabric,
wherein each of the branches provides access to data stored in local memory leaves by a remote cpu via a remote branch of the remote cpu over the ethernet switch fabric, without having to invoke a local cpu.
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This application is a continuation-in-part (CIP) application of U.S. application Ser. No. 15/179,120, filed Jun. 10, 2016, which claims the benefit of U.S. Provisional Patent Application No. 62/173,832, filed Jun. 10, 2015 and U.S. Provisional Application No. 62/186,284, filed Jun. 29, 2015.
This application is also related to U.S. application Ser. No. 15/629,229, entitled “Non-Uniform Memory Access (NUMA) Mechanism for Accessing Memory with Cache Coherence,”, U.S. application Ser. No. 15/629,247, entitled “Software Implemented Flash Translation Layer Policies,”, and U.S. application Ser. No. 15/629,218, entitled “Data Processing System with a Scalable Architecture over Ethernet,”. The disclosure of the above-identified applications is incorporated by reference herein in its entirety.
Embodiments of the present invention relate generally to data processing systems. More particularly, embodiments of the invention relate to scalable multi-processing systems.
As increasingly larger data sets become available for analysis, organizations such as businesses and governments need to be able to exploit that data for faster, more accurate decision-making and more efficient operation. Furthermore, processing such data sets may involve solving certain classes of problems that are both data intensive and computationally intensive. Certain such data sets may reach petabyte-scale in size and require a high degree of parallel processing throughput. However, conventional data processing systems fail to provide efficient or even tenable high bandwidth access to petabyte-scale data sets. Consequently, analysis performed by conventional data processing systems on such petabyte-scale data sets is typically inefficient and sometimes impossible given practical system constraints.
Embodiments of the invention are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements.
Various embodiments and aspects of the inventions will be described with reference to details discussed below, and the accompanying drawings will illustrate the various embodiments. The following description and drawings are illustrative of the invention and are not to be construed as limiting the invention. Numerous specific details are described to provide a thorough understanding of various embodiments of the present invention. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present inventions.
Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in conjunction with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification do not necessarily all refer to the same embodiment.
According to one aspect of the invention, a data processing system includes a number of central processing unit (CPU) subsystems, a number of memory complexes, and an Ethernet switch fabric coupled to each of the CPU subsystems and memory complexes. Each CPU subsystem includes one or more CPUs and one or more memory controllers corresponding to the CPUs. Each memory complex corresponds to one of the CPU subsystems. Each memory complex includes one or more branches and an array of memory leaves to store data. Each of the branches is coupled to one or more of the memory leaves and provides access to the data stored in the memory leaves. The Ethernet switch fabric is coupled to each of the memory controllers of the CPU subsystems and each of the branches of the memory complexes. Each memory controller can communicate with each of the branches via the Ethernet switch fabric over the Ethernet to access data stored in any of the memory leaves associated with the corresponding branch.
According to another aspect of the invention, a data processing system includes a number of processors, a number of memory controllers corresponding to the processors, a number of memory targets, and an Ethernet switch fabric coupled to the memory controllers and the memory targets. Each of the processors is coupled to each of the remaining processors via a processor interconnect, such as a Quick Path Interconnect™ (QPI). Each memory target includes one or more branches and a number of memory leaves managed by the branches. When a first memory controllers writes data to a first memory leaf via a first branch corresponding to the first memory leaf, the first memory controller sends a cache coherence message to at least one of the remaining memory controllers to indicate that the data stored in the first memory leaf has been updated. A second of the remaining memory controllers may determine whether the corresponding data has been previously cached in their corresponding local memory (e.g., dynamic random access memory or DRAM). If so, the second memory controller may communicate with the first memory controller and/or the first branch, for example, over the Ethernet, to fetch the newly updated data from the first memory leaf and to update its local memory.
According to another aspect of the invention, at least some of the functionalities of a flash translation layer (FTL) are maintained in a software layer or software stack, for example, hosted by an operating system (OS) for efficient management of the underlying flash memory devices. In one embodiment, a page virtualization table (PVT) and one or more block virtualization tables (BVTs) are maintained in upper level software such as a storage layer software hosted by an operating system. The PVT includes a number of PVT entries and each PVT entry maps a logical page number (LPN) to a virtual page number (VPN). Each BVT includes a number of BVT entries and each BVT entry maps a virtual block number (VBN) to a physical block number (PBN). When a request is received for accessing data stored in one of the flash memory devices, a first search is performed in the PVT based on a first LPN obtained from the request. A matching PVT entry is found based on the first LPN and a first VPN is obtained from the matching PVT entry. A second search is performed in a BVT based on the first VPN to locate a matching BVT entry that matches the first VPN. A first PBN is obtained from the matching BVT entry. An TO request is then issued based on the first PBN to a flash controller associated with a first flash memory device that stores data corresponding to the first PBN.
According to a further aspect of the invention, a data processing system includes one or more CPU subsystems and a number of memory complexes. Each CPU subsystem includes one or more CPUs and one or more memory controllers corresponding to the CPUs. Each of the memory complexes is associated with one of the CPU subsystems. Each memory complex includes one or more branches, a number of memory leaves to store data, and a replication interface. Each branch manages one or more memory leaves and each memory leaf includes one or more memory devices such as solid state memory devices. The replication interface automatically replicates data received from one of the CPU subsystems to another one of the memory complexes, where the data is stored in one of the memory leaves.
System Overview
Each CPU may include a cache such as cache 104 configured to operate with its local memory. The computing cores within the CPUs may each be configured to execute a software stack 106 resident either in local memory 105 or in a memory associated with memory root 108. A memory root may be configured to include one or more branches 112 connected through memory controllers 110 to one or more associated CPUs. In one embodiment, software stack 106 includes application programs, a database, block drivers, and/or wear level Reliability Availability Serviceability (RAS) modules.
The number of simultaneous data accesses that can be serviced by a computer in general limits the performance of many data driven applications. The disclosed system provides a large number of memory devices having a large net cross-sectional interconnect bandwidth coupled to a multi-rooted interconnection coupled to multiple CPUs housing the computing cores. The multi-rooted interconnection provides efficient parallel access to the data, thereby enabling concurrent, parallel, and multi-threaded application programs to operate efficiently. As stated previously, specialized system software manages the efficient scheduling of the computation and data access.
In one embodiment, root memory controller 110 connects to a complex of interconnected CPUs 100, each having multiple cores (e.g., processor cores), and drives a hierarchy of branches 112 and leaves 114. In one embodiment, there may be 15 processor cores within a CPU and each of the processor cores can execute instructions of a particular thread. Such a processor core may be referred to as a thread processor or processor core. Note that each branch is attached either to another branch or a number of leaves or a mix of both. A leaf such as leaf 114 is composed of flash memory or other solid-state or digital memory. In particular, there may be 1024 or more memory chips attached to a single root (e.g., implemented in field programmable gate array(s) or FPGA(s), application-specific integrated circuit(s) or ASIC(s)) through branches. Each CPU complex can be connected to one or more roots (e.g., eight or more roots). Consequently, if
The components in this architecture are composed of both hardware and software. Some of the components may include: (1) a data management system, the database or data management system may be (a) multithreaded, (b) configured to utilize a single shared memory model, or a distributed memory model, or a combination of both, in order to achieve a high degree of parallelism; (2) a memory management system, the memory management system may be (a) multithreaded to exploit large multi-cored systems, (b) highly parallel, (c) configured to access and manage a very large capacity (e.g., >>100 TB); (3) a cache management system, the cache management system may be configured to maintain data coherency across individual processing nodes (computing cores); and (4) a memory system comprising roots, branches and leaves.
Some embodiments may implement a cache coherent memory model in which each CPU thread caches its state in the memory. In one embodiment, there are four roots sometimes referred to herein as Memory Modules (MMs). Conceptually, each root replaces a memory riser card in the computer's chassis. The MMs connect to a distribution network, providing an interface to a number of branches, each of which connects to a number of leaves.
Conceptually, moving down the memory management system encompasses greater parallelism, effectively multiplying the concurrent operations at each level as memory access moves from the root to the branch to the leaves.
The disclosed system may be built in a variety of configurations that are suited to particular usage patterns. Embodiments of the invention may be optimized for a large number of specific uses such as these large memory consumption applications: Business Intelligence, Business Analytics, Geo-Seismic, Medical Imaging, Molecular and Biopharmaceutical Modeling (e.g. protein-protein interaction simulation), Social Networking and Patient Management.
In one embodiment, a shared memory fabric 116 implements a data network for transmitting messages between branches 112 in the system. The data network may be an Ethernet, in which branches may communicate with each other using Ethernet protocols. While depicted here in conceptual form, any technically feasible network structure or topology may be implemented, including non-blocking cross-bar and mesh topologies.
In one embodiment, since memory fabric 116 couple all of the branches 112, each of branches 112 can communicate with any one of the remaining branches for accessing any one of leaves 114 of the branch, without having to invoke an associated processing unit. According to one embodiment, each of the processing unit is coupled to any one of DRAMs 105 of all the processing units (e.g., CPUs 100(0) to 100(3)), for example, via a shared memory bus, interconnect, or network, without having to invoke a corresponding processing unit. Thus, a particular processor core of a particular processing unit can access any one of DRAMs 105 or any one of memory leaves 114 of any one of the remaining processing units, without having to invoke the associated processing unit. By coupling all branches together via a shared memory fabric (or interconnect, bus, or any kind of communication fabrics), a processor core can access data stored in any of the memory leaves using a number of access paths, which are represented by various branches. If one path (e.g., via a first branch) fails, a processor core can access the same data via another path (e.g., via a second branch).
In one embodiment, each GPU 190 includes a number of thread processors coupled to a cache 196. One or more thread processors may be configured to concurrently execute an instance of a thread program 194. A modern GPU may be configured to concurrently execute many thousands of instances of thread program 194 and retain execution state for yet more instances that may be scheduled for execution. In certain embodiments, different thread programs may be loaded into corresponding different GPUs or different GPU cores on the same GPU for concurrent execution.
GPUs 190 may be coupled to the cluster connect through any technically feasible interface. For example, GPUs 190 may be coupled to the cluster connect through a PCIe interface, a QPI (Intel Quick Path Interconnect) interface, or a memory bus interface.
In one embodiment, as described above, a data processing system includes a number of processing units or processors (e.g., CPUs) 100A-100B, a number of memory roots 108A-108B, and shared memory fabric or communication fabric 116 coupled to each of the memory roots. Each of the processing units 100A-100B include one or more processor cores (e.g., processor cores 121A-121B and 122A-122B), and each memory root is associated with one of the processing units. In this example, memory root 108A is associated with processor 100A and memory root 108B is associated with processor 100B. Each processor core may execute instructions of a particular thread, where a processor core is also referred to as a thread processor. Each of the memory roots 108A-108B includes one or more branches (e.g., branches 112A-112B) and a number of memory leaves (e.g., memory leaves 114A-114B). In this example, although there is only one branch for each processor, more branches can be implemented within the corresponding root. Each branch is associated with one or more memory leaves to provide access of the corresponding memory leaves. Each leaf includes one or more memory devices (e.g., solid state memory devices) to store data. The memory fabric 116 allows each of the branches 112A-112B to access (e.g., read and write) data stored in any of the memory leaves 114A-114B associated with any one of the remaining branches.
In one embodiment, each of branches 112A-112B includes one or more sets of queues (e.g., sets 123A and 124A, 123B and 124B) to buffer commands and data of accessing memory leaves, either locally or remotely. Each set of queues is associated with one of the processor cores of the corresponding processing unit. In one this example, the sets of queues 123A and 124A are associated with processor cores 121A-121B of processor 100A, one set for each of processor cores 121A-121B. Similarly, the sets of queues 123B and 124B are associated with processor cores 122A-122B of processor 100B, one set for each of processor cores 122A-122B. In one embodiment, each set of queues includes a submission queue or SQ (e.g., SQs 123A and 123B, also referred to as a command queue) and a completion queue or CQ (e.g., CQs 124A and 124B, also referred to as a done queue). A submission queue is used by an end point to submit a command to another end point over the shared memory fabric for a particular operation. A completion queue is used by an end point to place an acknowledgment or response to a command previously submitted via a submission queue.
For example, it is assumed the set of queues 125A is associated with processor core 121A. When processor core 121A attempts to access data stored in memory leaves 114A, it will place, via memory controller 110A, one or more commands in SQ 123A. Branch 112A then executes the commands from SQ 123A to perform the requested operation. Once the operation has been completed, branch 112A places a result (e.g., status, acknowledgement) of the operations in CQ 124A, which will in turn notify memory controller 110A and/or processor core 121A (e.g., via interrupt).
Similarly, when processor core 121A attempts to access data stored in memory leaves 114B, it places a command in SW 123A. Branch 112A then executes the command from SQ 123A. Branch 112A communicates with branch 112B via memory fabric 116 based on the command to request the operation to be performed at root 108B. In response branch 112B performs the requested operation. Once the operation has been completed, branch 112B communicates the result of the operation back to branch 112A. Branch 112A places the result in CQ 124A, which in turn will notify memory controller 110A and processor core 121A. Branches 112 and 112B may communicate with each other using a variety of signaling protocols or communication protocols (e.g., Ethernet protocols). Since there is one set of SQ and CQ for each of the processor cores, the above operations can be performed in parallel for multiple processor cores executing multiple threads.
In one embodiment, shared memory fabric 116 is configured to receive memory access requests from high-speed interface 170 and forward the requests to corresponding memory targets 164. For example, a CPU may generate a write request and post the write request to a memory controller 156. The memory controller may transmit the write request through high-speed interface 170 to shared memory fabric 116. Shared memory fabric 116 then forwards the write request to an appropriate memory target 164. Sequential chunks of memory (e.g. aligned cache lines) associated with a given CPU may be mapped to sequential units of storage within memory targets 164(0) through 164(T). Consequentially, when a given thread executing on one CPU core writes a contiguous range of memory, associated chunks of memory are distributed over the memory targets 164 rather than concentrated within on memory target. Spreading out each address range associated with each CPU core in this way statistically distributes accesses across interconnection and memory resources and reduces the probability of a resource contention where two or more CPUs are attempting to access a common resource along the path from memory interconnect 154 to stored data within memory targets 164. Shared memory fabric 116 is depicted here conceptually as a single module; however, the shared memory fabric may be implemented as a data network, such as a distributed mesh, a cross-bar, tree, and the like. Memory targets 164 may include branches 112, leaves 114, or a combination thereof.
A second memory complex 160(1) may be coupled to memory complex 160(0) through high-speed interface 172. In one embodiment, high-speed interface 172 is configured to transmit 120 GB/s of data in each direction, and may be implemented as twelve 10 GB Ethernet links or three 40 GB Ethernet links. Memory complex 160(1) may be configured to mirror operations of memory complex 160(0) or participate in data migration between memory complex 160(0) and 160(1).
Memory complex 160(1) may be coupled to memory complex 160(0) through high-speed interface 176. In one embodiment, high-speed interface 176 is configured to transmit 300 GB/s of data in each direction, and may be implemented as three 100 GB Ethernet links, or a combination of lower-rate Ethernet links.
The conceptual implementation shown here in
Embodiments of the present invention can be built in a variety of configurations that are suited to particular usage patterns. A particular configuration may be optimized for a large number of specific uses, such as these large memory consumption applications: Business Intelligence, Business Analytics, Geo-Seismic, Medical Imaging, Social Networking, Fraud Detection, Patient Management and Database and Data Warehouse Extract, Transform and Load (ETL), and protein-protein modeling.
In one embodiment, a root memory controller connects to a complex of interconnected CPUs, each consisting of multiple cores, and drives a hierarchy of branches and leaves. Observe that each branch is attached either to another branch or a number of leaves or a mix of both. Put another way, the memory controllers and branches may be interconnected. The interconnection may include the implementation of data coherence protocols utilized with and without multiple copies of the data distributed across local or remote leaves.
A leaf may include flash memory or other solid-state or digital memory. In particular, there may be 1024 or more memory chips attached to a single root (e.g., FPGA(s) or ASIC(s)) through branches. Each CPU complex can be connected to eight or more roots. Consequently, if this figure were accurate and to scale; the number of solid-state memory leaves would overwhelm the figure. In this architecture the CPUs have thousands of memory targets that may be accessed in parallel.
Embodiments of System Architectures
Referring to
Each of processor subsystems 501 may represent any of the CPU subsystems described above. Each processor subsystem may include one or more processors (e.g., processors 503A-503D, collectively referred to as processors 503) and each processor may include one or more processor cores. Each processor subsystem further includes a memory controller for one of the processors included therein such as memory controllers 504A-504D (collectively referred to as memory controllers 504). Each of processor subsystems 501 is coupled to any of remaining ones of processor subsystems 501 via a processor interconnect 102 (e.g., QPI interconnect).
Each of memory complexes 502 includes or is coupled to an Ethernet switch fabric such as Ethernet switch fabrics 211A-211D, collectively referred to as Ethernet switch fabrics 211. Ethernet switch fabrics 211A-211D may be the single Ethernet switch fabric that is coupled to each of the memory complexes 502, forming a shared memory fabric or an Ethernet 116. Each of memory complexes 502 further includes one or more branches and memory leaves such as branches/memory leaves 512A-512D (collectively referred to as branches/memory leaves 512). With shared memory fabric or Ethernet 116, each of memory controllers 504 and each of branches 512 can communicate with any one of the remaining ones of memory controllers 504 and each of branches 512.
Alternatively, each of memory controllers 504 can communicate with any one of the remaining memory controllers via processor interconnect 102. In one embodiment, each memory controller may determine a best route, either via processor interconnect 102 or via Ethernet fabric 106, to communicate with a remote counterpart (e.g., a remote memory controller or a remote branch), dependent upon the traffic congestion on the paths or routes. For example, when memory controller 504C wishes to access data stored in memory complex 502B, memory controller 504C can communicates with branches/memory leaves 512B via Ethernet switches 511B-511C over shared memory fabric/Ethernet 106 using Ethernet protocols. Alternatively, memory controller 504C can go through processor interconnect 102 to reach processor subsystem 501B which in turn reaches memory complex 502B.
Memory subsystem chassis 602 includes a number of memory subsystem slots to receive a number of memory subsystem blades 612A-612D (collectively referred to as memory subsystem blades 612) and one or more Ethernet switches 605. Each of memory subsystem blades 612 may represent any one or more of memory complexes 502 of
Each memory system may include roots, branches and leaves, as described above. In one embodiment, there are four roots sometimes referred to herein as Memory Modules (MMs). Conceptually, one or more roots can replace one or more corresponding memory riser cards in the computer's chassis. Each root may connect to a distribution network, providing an interface to a number of branches, each of which connects to a number of leaves.
In this embodiment, root 108 includes memory controller 110. Memory controller 110 includes one or more memory interface controllers 200(0) and 200(1) (collectively referred to as memory interface controllers 200) and one or more branch interface controllers 202(0) and 202(1), collectively referred to as branch interfaces controllers 202. Each of the branch interface controllers 202 includes cache or buffer 204 to buffer or cache data. Each of the branch interface controllers further executes or hosts a software stack such as software stacks 206 for performing a variety of operations such as memory accesses and routing. Note that each of memory interface controllers 200 can communicate with any of branch interface controllers 202, for example, via a DDR3 interface.
Each of memory interface controllers 200 is connected to an inter-processor data distribution network in which all CPUs have access to all memory. Associated memory may be implemented as a multi-rooted tree composed of branches and leaves as described in detail below. Associated computing resources may be implemented as a shared-memory multiprocessor, which may be of a uniform or non-uniform type.
In an alternatively embodiment, memory interfaces 200 may be implemented as a part of one or more memory controllers. Branch interfaces 202 may be implemented as a part of one or more branches, where each of memory controllers 200 is coupled to each of branches 202. Each branch is coupled one or more memory leaves 214(0)-214(1), collectively referred to as memory leaves 214.
In one embodiment, root 108 may be implemented with FPGAs that provide branch interface control. For example, an FPGA or an ASIC may execute software stack 206 that supports DDR3 memory accesses, target routing, Reliability Availability Serviceability (RAS) operations and various drivers e.g., a Non-Blocking Parallel Solid State Interface (NBPSI) as described in detail below. These operations may be distributed across many chips and subdivided into local processing steps, as shown in
In one embodiment, a Memory Master Controller (MMC) and Memory Slave Controller (MSC) devices are implemented with dedicated hardware. A root may represent an MMC, while a branch may represent an MSC and a leaf is a solid-state memory device. For example, Altera Stratix V FPGAs may be used for both the MMC and MSC. In this case, each FPGA has 48 serial links operating at 12.8 Gb/s, and three links from each MMC go to each of sixteen MSC devices. Each MSC in turn connects to 16 leaves, each a solid-state memory device, for example a 32 GB Single Level Cell (SLC) NAND Flash device. Many other implementations, including implementations in which the components and their interconnections are changing in real-time, are possible.
In an alternative embodiment, a memory branch as a parent branch is a component with a number of further or child branches organized as a hierarchy of branch layers, and leaves attached where each branch executes the same or a different software stack. In heterogeneous systems, each branch may be aware of its neighbors and cooperate in the implementation of the network drivers, RAS, error correction codes, database engines, data compression engines and solid-state drivers. Branches finally end in leaves. Each leaf is a device that acts to read and write data pages into a physical memory device, such as a non-volatile store. The leaf may be implemented in many forms using any technically feasible memory technology.
In one embodiment, approximately half of the memory system stores data and another half of the memory space supports rapid data access. In another embodiment, a fraction of the physical memory is reserved in order to provide adequate performance. In a further embodiment, the memory distributes data across individual leaves using specially designed methods that minimize inefficiencies. In another embodiment, the memory components themselves may be composed of individual components that together produce the desired behavior.
In a further embodiment, a segmented system with isolated domains that remain operative in the event of the failure of individual domains. These components are interdependent. In order for the whole system to function efficiently, the interconnected components depend on each other for correct functioning and timely completion of each other's work.
In one embodiment a virtual memory system is used to keep track of two sources of data from which a new file may be written. If an application program accesses a portion of an original file that the new file has not copied yet, this mechanism makes a copy on use (access). This way, large original files can be slowly migrated as new files without requiring large, slow copy operations. An advanced topic includes leaving both an original file and new instance of the file in place on reads, and just making a copy of the original file in response to high usage or in response to writes. This technique should implement a detection and recovery algorithm for when the files change enough or at a sufficiently rapid rate as to disallow continuation of this mechanism.
In one embodiment a mechanism is implemented to allocate a buffer using a memory device as a backing store, having a file the application wants to read on the same memory device and using copy-on-write (COW) for reads from the real file into space associated with the allocated buffer, instead of making a copy at read time. In a preferred implementation, a virtual memory system is configured to can keep track of two backing files depending on whether the data from the original file has only been read or has been modified.
Embodiments of Memory Subsystem with Replication Interface
Referring to
As described above Ethernet switch 116 is coupled to each of the memory controllers 156 and each of the memory targets 164, such that each memory controller (and its processor) can access any one of the memory targets 164 over the Ethernet. Each CPU subsystem is coupled to its memory target via a PCIe link. Each of CPU subsystems 150 includes one or more CPUs and each CPU includes one or more CPU cores. Each CPU may also be coupled any other CPUs via a processor interconnect such as a QPI link. Each of the memory controllers 156 may also be coupled to a local memory such as a DRAM (not shown) over a memory bus interface. Each of memory targets 164 includes one or more branches and each branch manages and controls one or more memory leaves. Each branch provides access to data stored in corresponding memory leaves. Each memory leave includes one or more solid state memory devices or chips.
In one embodiment, when shared memory fabric 116 receives data from a data source to be stored in one or more of memory targets 164, the data will be transmitted to the intended memory target(s). In addition, memory switch fabric 116 determines whether the data should also be replicated to another memory complex. Memory switch fabric 116 may examine the routing request or routing table maintained therein to determine whether a copy of the data should be replicated and where the copy should be replicated to, for example, using Ethernet protocols. The replication interface 825 could be used to replicate the same data to multiple memory complexes, similar to a multicast interface.
In one embodiment, most replication techniques have the CPU send a page to a local storage and then replicate it to some remote place. An embodiment of the invention defines a mechanism to do so simultaneously by use Ethernet as the transport to both the local and remote device.
Embodiments of the invention enable efficient architectural scale-out of both the computational capacity and the corresponding memory capacity. One form of scale-out involves adding CPU subsystems configured as independent computation-server boxes. The shared memory fabric maintains cache coherence among different CPUs that reside within the independent servers. In some embodiments the memory fabric transports cache coherence messages. In other embodiments the access to particular leaves is restricted to particular servers.
Embodiments of Cache Coherence Memory Models
Referring to
In one embodiment, each of memory controllers 156(0) and 156(1) includes a cache memory unit (CMU) such as CMUs 210(0) and 210(1) respectively, collectively referred to as CMUs 210. CMUs 210 communicate with each other to maintain cache coherency amongst multiple memory subsystems and memory controllers. When a memory controller writes data to its memory complex, a CMU associated with the controller sends a cache coherence message to another CMU of another memory controller to notify the remote memory controller that there is an update on the data stored in a storage device. If the remote memory controller has previously cached the same data in its local memory, the remote memory controller may fetches the data from the storage device to update its local memory.
For example, when memory controller 156(0) writes data from its local memory 105(0) to memory leaves 114(0), CMU 210(0) sends a cache coherence message to CMU 210(1) via Ethernet switch fabric 116 or processor interconnect 102. In response to the cache coherence message, CMU 210(1) determines whether the data stored in the same storage location has been previously cached in its local memory 105(1). If the data has been previously cached in local memory 105(1), CMU 210(1) fetches the data from memory leaves 114(0), for example, by invoking branch 112(0) via Ethernet switch fabric 116.
As shown, PVT data 221, block virtualization table (BVT) data 222, and target data 223 may reside within a memory target 164. PVT data 221 and/or BVT data 222 may need to be managed within a cache coherence regime and may further need to be queried in conjunction with overall cache management.
In one embodiment, DMU 230 is implemented using an application-specific logic circuit. In other embodiments, DMU 230 is implemented as a combination of non-volatile, computer-readable microcode and an embedded processing engine, the microcode being configured to direct an embedded processing engine to perform the functions of DMU 230. In alternative embodiments, DMU 230 may be implemented in data network components, for example data network components linking MMC 301 and MSC 302.
This system is representative of multiprocessor systems connected in a Non-Uniform Memory Architecture (NUMA) configuration with high-speed, point-to-point, cache-coherent memory interconnects. NUMA affinity refers to the practice of accessing data that is physically located on memory which has the least performance penalty induced by the non-uniformity of the memory architecture as seen by the core executing code. For optimal READ performance, the data should be transferred using Direct Memory Access (DMA) to the node that has the user buffer, in order to minimize the QPI traffic between nodes. Apart from the performance issues, there is one additional performance issue to minimize queuing delay for READs.
In one embodiment, a software driver module allocates READ operations on any of the processor cores in order to minimize the queuing delay for READ operations. However, the completion (DMA transfer) of the READ data will always be done on the node where the destination READ buffer resides. To achieve this, there will be one completion queue per core and the destination completion queue will be on the same NUMA node as the destination user buffer. Consequently, there will be no lock contention on the completion queue.
Embodiments of Software Implemented FTL Policies
In one embodiment, software stack 801 includes an FTL module performing any of the FTL operations at a software level. A conventional FTL functionality is typically implemented at a lower level (e.g., within a flash memory device of a memory complex) or as a part of a flash controller (e.g., flash controllers 821A-821B). Access to the FTL layer in a conventional system may block another access to the FTL layer because of a limited number of IO requests available in parallel (e.g., 72 IO requests). By maintaining FTL module 811 in software stack 801, the number of IO requests that can be issued in parallel can be significantly increased (e.g., 8000 IO requests), without blocking access of other flash memory devices.
In one embodiment, software stack 801 further includes PVT 812 and one or more BVTs 813. PVT 812 and BVTs 813 may also be maintained by FTL module 811 according to an alternatively embodiment. PVT 812 and BVTs 813 are utilized by FTL module 811 to access memory leaves 822A-822B via the corresponding flash controllers 821A-821B of memory complex 802A. Note that software stack 801 may be coupled to a number of memory complexes such as 802A-802B.
A page virtualization table or PVT, such as PVT 812, is a multi-level table that contains the translation of a logical page to a flash page. The PVT table is initialized during a system startup phase (e.g. driver startup) and stores an entry for each logical page in the system. The number of entries is generally equal to the logical size of the block device in pages. Each entry in the PVT stores a logical page number, the corresponding flash page number, a sequence number and a bit to indicate if the page is valid or trimmed. The PVT may be reconstructed from flash memory by reading the metadata portion of every flash page when the driver is loaded during the initialization of the system.
In some embodiments of the invention data stored in solid-state memory (for example flash) moves independent of the file system. Consequently, a PVT may be used to move the data (stored in pages) while leaving the file system meta-data unchanged. In a large system, this table is often huge (e.g. 6 terabytes (TB) for a 64-bit page virtualization table in a system with 3 PBs of capacity). In order to reduce the table size, table entries are “shared.” In a first entry a 64-bit quantity is stored and in subsequent “shared” entries 16-bit offsets are stored. In one embodiment with shared entries for 16 pages, the table can be a third of the unshared size and so on. The pages must be close enough to use the small (16 bit) offsets, there must not be contention for the data structures, and the data must be temporally distributed so it can be read in parallel. In one embodiment one core of a CPU has exclusive access to a subset of page table entries, and that subset is non-contiguous (table entries) so that subsequent accesses will still be distributed across the cores.
A block virtualization layer or table, such as BVTs 813, abstracts physical block addresses from the driver stack and provides a virtually contiguous range of flash block addresses. The first initialization of the device identifies and stores any factory marked bad blocks. A BVT excludes these blocks and creates a virtually contiguous range for the physical addresses. During the course of normal operation, more unusable blocks may be identified and more blocks may become unusable over time and be subsequently identified. A block virtualization layer of the software system remaps virtual blocks residing on failed physical blocks to new physical blocks.
Conceptually, a BVT is below the PVT and translates a flash virtual block number to a physical block number. The virtual page number includes the virtual block number and the page index in a flash block (e.g., a page number or offset within a physical block). In one embodiment, the PVT uses 42 bits to store a flash virtual page number (FVPN). If the FVPN is represented as a block, page index tuple, then 32 bits are used for the block number and 8 bits are used for the page index. These 40 bits of page address cover 2.5 PB of virtual space. This fits easily within the 42 bits available allocated for virtual page numbers in the PVT. The physical page number itself will not be exposed outside the topology and the block virtualization layer.
In one embodiment, referring now to
Based on the VBN, FTL module 811 looks up in BVT 813A to locate a BVT entry that matches the VBN and to obtain a physical block number (PBN) from the matching BVT entry. Based on the PBN, an IO request is issued and sent down to flash controller 821A. The IO request may include the PBN and a page number obtained from the VPN). The page number specifies a page (or an offset) within a physical block indicated by the PBN in flash memory device 825A. In response, flash controller 821A accesses the specified page of the physical block in one of the LUNs 823.
In a conventional system, the PVT 812 and BVTs 813 are maintained by a flash controller. When an IO request is issued, other IO requests maybe blocked to access PVT 812 and BVTs 813 in order to determine the physical block numbers. As a result, the number of IO requests that can be issued in parallel may be limited (e.g., 72 IO requests). By maintaining PVT 812 and BVTs 813 in software stack 801, the mappings of physical blocks are performed within software stack 801 in a non-blocking manner. When an IO request is sent down to a flash controller, the physical block number of a LUN has already determined. The flash controller can simply access the requested LUN based on the IO request. Other IO requests for accessing other regions of the same LUN or other LUNs are not blocked. As a result, the number of IO requests that can be sent down in parallel can be significantly increased (e.g., 8000 IO requests).
In addition, according to one embodiment, by maintaining the PVT 812 and BVTs 813 within software stack 801, the access patterns of the flash memory devices can be monitored and tracked. For example, based on the access patterns, a storage manager (not shown) can determine which storage regions are frequently accessed regions (e.g., hot regions or cold regions), what kinds of accesses (reads or writes, distribution of reads and writes like percentages of reads vs. writes), a sequence of the accesses, or workloads of the memory devices, etc. Based on this information, a quality of service (QoS) policy may be selected and applied. More IO requests can be issued in parallel if accesses to different regions are requested. A garbage collection process can be also be initiated on the flash memory devices based on the workloads, which can be determined based on the tracking information.
The workload information can also be utilized for route selections for accessing data stored in a memory device via a number of routes. For example, if a local memory controller attempts to access data stored in a local memory (e.g., DRAM) and its path to the local memory is busy (e.g., based on the access workload), the local memory controller may communicate with a remote memory controller to fetch the same data from the local memory via a processor interconnect. Alternatively if the same data is also stored in a flash memory device, the remote memory controller can fetches the data from the flash memory device. The remote memory controller can then send the data to the local memory via the Ethernet.
Similarly, if a local processor attempts to read data from a remote memory (e.g., DRAM) and to save the data to a local flash memory device, the local processor communicates with a remote processor via a processor interconnect. The remote processor and a remote memory controller read the data from the remote memory. The remote memory controller sends the data to a local memory controller over the Ethernet and the local memory controller saves the data to the local flash memory device.
The architecture as described throughout this application can be expanded by adding more processor subsystems and/or memory subsystems by coupling them over the Ethernet fabric. As larger and larger datasets must be handled, more and more memory capacity may be required. A mechanism as described above for increasing the memory capacity by utilizing many interconnected memory fabrics, connected either through the processor interconnect (e.g. a Quick Path Interface (QPI), a memory interface (e.g. DDR3 or DDR4), and/or a high speed peripheral interconnect (e.g. PCIe or RapidIO™) is required. This mechanism allows parallel access to the memory fabric through individual memory controllers connected to the appropriate interfaces in the distributed computing nodes. With a sufficient number of nodes the memory capacity can be suitably adjusted. This mechanism also allows parallel access to the memory fabric through individual memory controllers connected to the appropriate interfaces in the distributed computing nodes. With a sufficient number of computing nodes the computing power can be suitably adjusted.
One embodiment implements a mechanism that provides a consistent memory model for multiple computing nodes that share data, in order to provide parallel processing to the shared data. This mechanism provides a consistent memory model to each node and can be implemented either at the memory controller, using the memory fabric interconnect, or in the memory fabric itself. A consistent memory model insures each computing unit that accesses the data in the memory “sees” data that was (or is) valid at the time of access. This guarantee exists because all cached data, by which the system maintains a memory content which may be maintained in multiple locations simultaneously, is maintained in a coherent manner. In the case of multiple memory controllers attached to multiple computing nodes, copies of the same memory contents stored in multiple memory controllers or on multiple memory chips must be synchronized.
In one embodiment, the memory controller contains a cache management unit (CMU) that receives data from the leaves attached to branches. The leaves all contain a data management unit (DMU). The DMU maintains a coherent mapping of the page and block addresses of the data in the leaf. Access to the data is recorded in a directory of memory controller cache units that may modify the data. If a memory controller attempts a modification, the cached copy of the data in other memory controllers is invalidated by the leaf DMU.
One embodiment implements a mechanism to provide for multiple computing nodes that share metadata, in order to provide parallel processing of the underlying shared data. Embodiments may separate the management of the data coherence from the management of the metadata coherence. This mechanism provides a consistent metadata management model to each node and can be implemented either at the memory controller, using the memory fabric interconnect or in the memory fabric itself. A consistent metadata management model insures metadata management operations (e.g. free space recovery, error correcting code generation and decoding, etc.) that access the metadata describing the data in the memory, all access metadata that was (or is) valid at the time of access. This guarantee exists because all cached metadata, by which we mean metadata that may be maintained in multiple locations simultaneously, is maintained in a coherent manner. In the case of multiple memory controllers attached to multiple computing nodes, copies of the same metadata stored in multiple memory controllers or on multiple memory chips must be synchronized.
The management of solid-state memory devices implements mechanisms for the remapping of memory addresses onto the underlying chips so that failed chips may be replaced or bypassed, among other eventualities. The original mapping is accomplished by maintaining the metadata in a PVT. Portions of the metadata describing the mappings of the data on a particular leafs memory chip (or chips) may be divided among the memory controllers such that a particular memory controller maintains the metadata for a subset of the entire system, and all the memory controllers, taken as a group, contain the required metadata for all the chips. The division of the metadata is done in a way that enables the distribution of data on memory leaves in a way that allows for the subsequent parallel access of the data.
Alternative Embodiment of Data Processing Systems
As shown, each processor 1832 may be coupled to one or more memory controllers (MCs) 1836 within the interface complex 1834. In one embodiment, a memory controller 1836 corresponds to a memory controller 110 of
Memory complex 1850 includes flash controllers 1852 and memory subsystems 1854. Each flash controller 1852 may be coupled through a memory interface 1851 to a corresponding memory subsystem 1854. In one embodiment, each flash controller 1852 is coupled to a number of memory subsystems 1854. Each memory subsystem 1854 may include one or more integrated circuit memory devices. In one embodiment, each memory subsystem 1854 includes one or more flash memory devices. In another embodiment, one or more memory subsystems 1854 include DRAM memory devices. In certain embodiments, each memory subsystem 1854 corresponds to leaf 114 as described above.
During normal operation, memory access requests are generated by the processors 1832. The memory access requests are transmitted through memory controllers 1836, and forwarded by switches 1842 to appropriate flash controllers 1852. Each flash controller 1852 directs a given memory access request to an appropriate memory subsystem 1854, where data associated with the memory access request resides. A memory access request acknowledgement is returned from the flash controller 1852. A given acknowledgement may include a block of data requested by a memory read request, or a write acknowledgement in response to a memory write request. Caching may be implemented within the memory controllers 1836, switches 1842, flash controllers 1852, or any combination thereof. In certain embodiments, write caching may provide a lower latency acknowledgement to a write request generated by a processor 1832. For example, in one embodiment, memory controllers 1836 implement write caching, whereby a write completion acknowledgement is transmitted back to a processor 1832 from a memory controller 1836 prior to associated data being written to a corresponding target memory subsystem 1854.
In one embodiment, each memory controller 1836 is configured to provide a request queue to accommodate a number of pending memory requests generated by multiple processor cores and/or multiple process threads associated with each processor 1832. Queue priority may be given to read requests over write requests bound for the memory complex 1850, whereas write acknowledgements may be given priority over read acknowledgements for acknowledgements bound for the processor complex 1830. Accommodating multiple pending memory access requests (e.g., concurrent, outstanding read requests and write requests) creates multiple design consequences and requirements for memory controllers 1836.
In one embodiment, a memory address generated by a process executing on processor 1832 is remapped from a data address space (DAS) to a flash virtual address (FVA) space, and is further mapped to a flash virtual page number (FVPN), and finally is mapped to a flash physical address space (FPAS). A portion of the remapping may be performed by processor 1832, memory controller 1836, switch 1842, flash controller 1852, or any combination thereof.
Embodiments of computing system 1800 need to operate in configurations that are significantly larger in scale (e.g., orders of magnitude larger) than conventional computer systems, while preserving common access for each processor 1832 to large-scale data, which may reside in memory complex 1850. As a consequence of large processing scale, unconventionally large memory scale for application data, and a requirement to provide shared access to potentially all application data residing within memory complex 1850 to all processes executing within processors 1832, certain additional design features may be advantageously implemented within computing system 1800. Such design features are not conventionally required in typical computing systems. Specific design features associated with efficient performance at large scales include: (1) scalable paging operations, (2) scalable allocation and utilization of memory capacity, (3) scalable memory page and block operations to accommodate large, low latency read and write operations, (4) data protection for large data sets, and (5) performance optimizations for solid-state memory related to operational constraints associated with conventional solid-state memory devices (e.g., flash memory).
More specifically, large-scale computing over multiple processors with multiple execution threads will generally generate a large number of concurrent, independent memory access requests. Such memory access requests may be directed to a shared data image of application data in memory complex 1850, resulting in extremely intensive access utilization relative to conventional computing systems.
Furthermore, because a given application data footprint may be orders of magnitude larger (e.g., hundreds of terabytes through hundreds of petabytes) than a conventional application data footprint comprising less than a terabyte, computing system 1800 advantageously implements data protection for the application data. Data protection in such a setting may be extremely helpful because the physical memory soft error rate for hundreds of terabytes of data in prevailing solid-state memory technology could yield many errors during the execution time of target applications. Certain memory device technologies may even cause multiple, concurrent errors at a relatively frequent rate, leading to a need for two or more layers of data protection. In certain settings, entire blocks of data may be corrupted or “erased,” requiring the implementation of an erasure code or technical equivalent to provide data protection and recovery. For example, if a solid-state flash memory device comprising memory subsystem 1854 fails or if a block of data therein is corrupted, a block of data is lost (e.g., erased). An erasure code may be implemented to recover blocks of data, such as the block of data lost in the above example. Failure events leading to significant loss of data are sufficiently rare that conventional systems designers are not motivated to develop features to address such failure events. However, with active, solid-state memory hosting application data sized in the hundreds of terabytes to many petabytes, data protections becomes highly advantageous if not essential for the proper operation of computing system 1800.
In certain embodiments, computing system 1800 may implement scalable paging operations to accommodate very high throughput, low-latency memory operations associated with processors 1832 accessing memory complex 1850. Specifically, computing system 1800 may implement a mechanism for providing compact virtual page tables implemented to perform different address space mappings (e.g., the DAS to FVA, to FVPN to FPAS mapping discussed above). Because the target block range within memory complex 1850 is so large, conventional virtual page mapping techniques would result in large, inefficient mapping tables. A virtual page mapping technique is disclosed herein that reduces overall table size for greater memory access and execution efficiency.
Furthermore, computing system 1800 may implement lockless queues for transmitting commands and command completion acknowledgments between two processors without either processor needing to block execution progress provided there is space in the queue. In one embodiment, a lockless queue is implemented as a circular buffer.
In certain embodiments, computing system 1800 may implement scalable allocation and utilization of memory capacity to accommodate an extremely large application data footprint. Specifically, computing system 1800 may implement a mechanism for moving live (allocated to active application processing) blocks within the memory complex 1850 without processor intervention. Such a move operation is referred to herein as a migration pivot. In one embodiment, the migration pivot is implemented to accommodate data protection. Furthermore, computing system 1800 may implement distributed read copy operations in preparation for an erase operation to enable high-performance read operations. This operation may allow a memory complex 1850 comprising flash memory devices to efficiently service read/write requests from the processor complex 1830, while also reclaiming and preparing pages to be newly written. Computing system 1800 may also implement a trim range function to operate in conjunction with one or more file systems residing within memory complex 1850.
In one embodiment, memory complex 1850 is configured to store data blocks associated with application data, as well as associated virtual mapping tables/virtualization tables, bad block information, trim information, and other data technically relevant to operation and reconstruction of data within memory complex 1850. By storing virtualization maps, bad block maps, and the like, within the same protected data set as target data, a full recovery of data and virtual mappings associated with memory complex 1850 may be advantageously performed using only data available on memory complex 1850. As one example of this technique, By contrast, many conventional memory systems store virtualization tables independently of target data, creating inefficiencies during recovery.
In certain embodiments, computing system 1800 may implement scalable memory page and block operations to accommodate large, low latency read and write access to memory complex 1850. These operations are implemented to achieve high utilization of total cross-sectional bandwidth over every available memory subsystem 1854 within memory complex 1850, thereby providing extremely high memory bandwidth to processor complex 1830. In one embodiment, a massively parallel memory architecture enables scalable memory page and block operations. In certain embodiments, a DRAM cache provides read-ahead caching and reconstruction-related computation resources, which may, for example, be implemented within each of the memory controllers 1836. One embodiment provides for fast acknowledgment of write operations through write buffering in a DRAM buffer followed by an acknowledgement prior to write data being written to a designated target. The DRAM buffer may be implemented within the memory controllers 1836. Alternatively, the DRAM buffer may be implemented within system memory (not shown) associated with, or coupled directly to, processors 1832.
In conventional systems, memory access performance is typically constrained by system efficiencies when handling larger (e.g., 8 MB) block access requests. Operating systems may provide for asynchronous operations, but overhead associated with managing large block access requests may eliminate any efficiencies gained by performing asynchronous input/output operations. In one embodiment, a technique for multiple, concurrent input/output operations improves performance associated with performing large input/output operations, such as large block reads/write operations by distributing associated workload over multiple cores comprising one or more processors 1832.
Read performance may be improved by a technique referred to herein as “read-around,” whereby a block of data associated with a busy memory resource comprising a memory subsystem 1854 is reconstructed rather than read. A memory resource may be busy because a block comprising the memory resource is being written. The memory resource may include a sub-circuit referred to herein as a LUN. In certain scenarios, writing a block of data takes considerably longer (e.g., 20× longer) than reconstructing the block of data. Therefore, the read-around technique may provide a performance advantage compared to waiting and performing a direct read of the target data. In certain embodiments, write operations are scheduled to advantageously facilitate read-around opportunities to improve average read performance. In one embodiment, memory bandwidth is offered to different memory controllers 1836 according to available bandwidth for each. Available bandwidth may represent a fixed system characteristic or a prevailing workload.
In certain embodiments, computing system 1800 may implement data protection for large data sets. In one such embodiment, computing system 1800 may implement data protection in conjunction with sequence numbers to enable re-creation of a page virtualization table (PVT) in the event of a system crash. In one embodiment, computing system 1800 may implement adaptive data protection for different failure characteristics according to a system lifetime. For example, a system may initially operate with a less conservative protection scheme and transition to a more conservative protection scheme at some point in operational time. In certain settings, garbage collection interacts with a data protection scheme. This interaction is further complicated by practical requirements associated with needing to erase flash memory prior to writing the flash memory. In one embodiment, computing system 1800 implements a round-robin allocation system for writing blocks during garbage collection, and a reclamation mechanism that may be triggered according to a free-space threshold. In one embodiment, continuous data protection and continuous garbage collection are provided by adaptively balancing application access requests and garbage collection activities. The above techniques advantageously enable computing system 1800 to efficiently operate at high performance levels while providing a high degree of data protection. As discussed previously, data protection becomes highly advantageous given the scale of application memory footprints supported by the computing system 1800.
In certain embodiments, computing system 1800 may implement performance optimizations for solid-state memory related to operational constraints associated with conventional solid-state memory devices (e.g., flash memory). One constraint relates to read and/or write “disturbance” associated with accessing adjacent blocks of data within a flash device. In one embodiment, an efficient command processing circuit module implements an access abstraction that includes a set of state machines for implementing detailed access control signaling to flash devices comprising memory subsystems 1854. Certain embodiments of computing system 1800 require a high degree of fault tolerance for highly-available computing and therefore implement component-level redundancy.
The above techniques and embodiments may be implemented independently in various systems architectures, however they may be advantageously implemented together within computing system 1800 to provide a high-performance, high availability computation platform for executing applications requiring unconventionally large application memory footprints.
Some portions of the preceding detailed descriptions have been presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the ways used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of operations leading to a desired result. The operations are those requiring physical manipulations of physical quantities.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the above discussion, it is appreciated that throughout the description, discussions utilizing terms such as those set forth in the claims below, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.
Embodiments of the invention also relate to an apparatus for performing the operations herein. Such a computer program is stored in a non-transitory computer readable medium. A machine-readable medium includes any mechanism for storing information in a form readable by a machine (e.g., a computer). For example, a machine-readable (e.g., computer-readable) medium includes a machine (e.g., a computer) readable storage medium (e.g., read only memory (“ROM”), random access memory (“RAM”), magnetic disk storage media, optical storage media, flash memory devices).
The processes or methods depicted in the preceding figures may be performed by processing logic that includes hardware (e.g. circuitry, dedicated logic, etc.), software (e.g., embodied on a non-transitory computer readable medium), or a combination of both. Although the processes or methods are described above in terms of some sequential operations, it should be appreciated that some of the operations described may be performed in a different order. Moreover, some operations may be performed in parallel rather than sequentially.
Embodiments of the present invention are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of embodiments of the invention as described herein.
In the foregoing specification, embodiments of the invention have been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.
Venkataraghavan, Vikram, Carlson, Rick, Himelstein, Mark, Wilford, Bruce, Wilde, Todd, Durai, Vishwas, Barnett, Blair, Rowett, Kevin, Van Gaasbeck, Richard
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